The present invention relates to a light-emitting element device for use in image input sections of such apparatuses as facsimile machines and image scanners. More particularly, it is directed to a light-emitting element device, a method of manufacturing such a light-emitting element device whose light-emitting layer can be formed by a thick-film process which allows inexpensive fabrication, and an image reading device using such light-emitting element device.
To miniaturize image reading devices, what has recently been proposed is an image reading device having its light-emitting element and light-receiving element formed integrally with each other using such a solid-state light source as an electroluminescent (EL light-emitting) element in place of a fluorescent lamp.
In the image reading device of such type, rays of light irradiating the surface of a document are introduced or injected at a right angle thereto in order to prevent illumination from being nonuniform. In addition, in order to shorten the length of an optical path for the light reflected from the document surface to be injected to the light-emitting element, e.g., an EL light-emitting element device 40 is arranged immediately above a light-receiving element array 30 through an adhesive 50 as shown in FIGS. 9 and 10, the light-receiving element array 30 consisting of line-like extending light-receiving elements 31. Light-transmitting portions 60 are formed on the El light-emitting element device 40 at positions corresponding with the respective light-receiving elements 31, so that rays of reflected light 80 from a document surface 70 can be guided into the respective light-receiving elements 31 through the corresponding light-transmitting portions 60.
Each light-transmitting portions 60 of the EL light-emitting element device 40 has the following structure. A transparent electrode 42, an insulating layer 43, a light-emitting layer 44, an insulating layer 45 are sequentially deposited on a transparent substrate 41 by a thin-film process, and a metal electrode 46 is further deposited and then patterned so as to have a rectangular opening portion 46a by etching. Since the transparent electrode 42, the insulating layer 43, and the light-emitting layer 44 are made of light-transmitting members, respectively, a portion locating immediately above the opening portion 46a provided on the metal electrode 46 constitutes a light-transmitting portion 60.
However, the above structure uses thin-film type EL light-emitting elements, and this not only increases the fabrication cost but also limits the surface area of each EL light-emitting element due to such restraints as the size of a vacuum chamber used during the thin-film process, thus making it difficult to obtain sufficiently large-sized EL light-emitting elements.
There are EL light-emitting elements whose light-emitting layer is formed by a thick-film process such as screen printing. Although an EL light-emitting element of this type provides a solution to the above problem, it imposes another problem. Specifically, since its light-emitting layer is made of a material in which fluorescent light-emitting particles such as ZnS:Cu or Al are dispersed into an organic binder such as cyanoethylpolyvinyl alcohol (CEPVA), the light-emitting layer does not transmit the reflected light from the document surface efficiently, causing the reflected light to scatter due to a difference in refractive index between the light-emitting particles and the organic binder. As a result, if an EL light-emitting element of a thick-film type is applied to the above-described image reading device integrating its light-emitting element and light-receiving element, then the light-emitting layer portion in the light-emitting element must also be removed. However, the organic binder contained in the light-emitting layer is so highly water-permeable, absorptive, and soluble to organic solvents that it is poor in resistance to etching. In addition, the light-emitting layer deposited by a thick-film process has a thickness of 10 to 100 .mu.m, which does not permit fine patterning. Thus, mere replacement of the EL light-emitting element portion with a thick-film type is not a solid solution to improving the structure and method of manufacturing the exemplary conventional image reading device.